Magnetic recording medium with multiple exchange coupling layers and small grain magnetic layers

ABSTRACT

A magnetic recording medium is provided that includes a recording layer structure including a first magnetic recording layer, a second magnetic recording layer, a third magnetic recording layer, a fourth magnetic recording layer, and a plurality of nonmagnetic exchange coupling layers. The first magnetic recording layer is closest to a substrate and the fourth magnetic recording layer is farthest from the substrate. An amount of Co in the first magnetic recording layer is greater than or equal to the amount of Co in the second magnetic recording layer, the third magnetic recording layer, and the fourth magnetic recording layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.15/912,648, filed on Mar. 6, 2018, which is a continuation of U.S.patent application Ser. No. 14/644,633, filed on Mar. 11, 2015, now U.S.Pat. No. 9,934,808, the entirety of which are incorporated by referenceherein for all purposes.

BACKGROUND

The present application relates to magnetic recording media, and morespecifically, this invention relates to a recording layer structurehaving small grain magnetic recording layers separated by exchangecoupling layers, which may be of particular use in perpendicularmagnetic recording (PMR) media, shingle-written magnetic recording (SMR)media, and magnetic field-assisted magnetic recording (MAMR) media.

The heart of a computer is a magnetic hard disk drive (HDD) whichtypically includes a rotating magnetic disk, a slider that has read andwrite heads, a suspension arm above the rotating disk and an actuatorarm that swings the suspension arm to place the read and/or write headsover selected circular tracks on the rotating disk. The suspension armbiases the slider into contact with the surface of the disk when thedisk is not rotating but, when the disk rotates, air is swirled by therotating disk adjacent an air bearing surface (ABS) of the slidercausing the slider to ride on an air bearing a slight distance from thesurface of the rotating disk. When the slider rides on the air bearingthe write and read heads are employed for writing magnetic impressionsto and reading magnetic signal fields from the rotating disk. The readand write heads are connected to processing circuitry that operatesaccording to a computer program to implement the writing and readingfunctions.

The volume of information processing in the information age isincreasing rapidly. Accordingly, an important and ongoing goal involvesincreasing the amount of information able to be stored in the limitedarea and volume of HDDs. Increasing the areal recording density of HDDsprovides one technical approach to achieve this goal. In particular,reducing the size of recording bits and components associated therewithoffers an effective means to increase areal recording density.

However, the continual push to miniaturize the recording bits andassociated components presents its own set of challenges and obstacles.For instance, as the size of the ferromagnetic crystal grains in amagnetic recording layer become smaller and smaller, the crystal grainsmay become thermally unstable, such that thermal fluctuations result inmagnetization reversal and the loss of recorded data. Increasing themagnetic anisotropy of the magnetic particles may improve the thermalstability thereof, yet ultimately reduce the ability to writeinformation thereto. Accordingly, increasing the magnetic anisotropy ofthe magnetic particles may also require increasing the switching fieldneeded to switch the magnetization of the magnetic particles during awrite operation.

According to one embodiment, a magnetic recording medium includes: asubstrate; and a magnetic recording layer structure formed above thesubstrate. The magnetic recording layer structure includes: a firstrecording magnetic layer having a first magnetic anisotropy field(H_(k)) value greater than or equal to about 20 kOe; a first nonmagneticexchange coupling layer formed above the first magnetic recording layer;a second magnetic recording layer formed above the first nonmagneticexchange coupling layer, the second magnetic recording layer having asecond H_(k) value that is less than or about equal to the first H_(k)value of the first magnetic recording layer; a second nonmagneticexchange coupling layer formed above the second magnetic recordinglayer; a third magnetic recording layer formed above the secondnonmagnetic exchange coupling layer, the third magnetic recording layerhaving a third H_(k) value that is less than or about equal to the firstH_(k) value of the first magnetic recording layer; a third nonmagneticexchange coupling layer formed above the third magnetic recording layer;a fourth magnetic recording layer formed above the third nonmagneticexchange coupling layer, the fourth magnetic recording layer having afourth H_(k) value that is less than or about equal to the first H_(k)value of the first magnetic recording layer; a fourth nonmagneticexchange coupling layer formed above the fourth magnetic recordinglayer; and a fifth magnetic recording layer formed above the fourthnonmagnetic exchange coupling layer, the fifth magnetic recording layerhaving a fifth H_(k) value that is less than or about equal to the firstH_(k) value of the first magnetic recording layer.

According to another embodiment, a magnetic recording medium includes: asubstrate; and a magnetic recording layer structure formed above thesubstrate. The magnetic recording layer structure includes five or moremagnetic recording layers and four or more nonmagnetic exchange couplinglayers, where the magnetic recording layers and the nonmagnetic exchangecoupling layers are arranged in an alternating pattern, and where themagnetic recording layers are separated from each other by least one ofthe nonmagnetic exchange coupling layers. The magnetic recording layerpositioned closest to the substrate has each of the following: anaverage magnetic grain pitch of about 8.3 nm or less, a magneticanisotropy field (H_(k)) value of greater than or equal to about 20 kOe,and a thickness that is about 40% of a total thickness of the magneticrecording layer structure.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a disk drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., hard disk) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a simplified drawing of a magnetic recording disk drivesystem, according to one embodiment.

FIG. 2A is a cross-sectional view of a perpendicular magnetic head withhelical coils, according to one embodiment.

FIG. 2B is a cross-sectional view a piggyback magnetic head with helicalcoils, according to one embodiment.

FIG. 3A is a cross-sectional view of a perpendicular magnetic head withlooped coils, according to one embodiment.

FIG. 3B is a cross-sectional view of a piggyback magnetic head withlooped coils, according to one embodiment.

FIG. 4 is a schematic representation of a perpendicular recordingmedium, according to one embodiment.

FIG. 5A is a schematic representation of a recording head and theperpendicular recording medium of FIG. 4, according to one embodiment.

FIG. 5B is a schematic representation of a recording apparatusconfigured to record separately on both sides of a perpendicularrecording medium, according to one embodiment.

FIG. 6 is a schematic representation of a perpendicular magneticrecording medium comprising three exchange coupling layers, according toone embodiment.

FIG. 7A is a schematic representation of a perpendicular magneticrecording medium comprising at least four exchange coupling layers,according to one embodiment.

FIG. 7B is a schematic representation of a perpendicular magneticrecording medium comprising at least five exchange coupling layers,according to one embodiment.

FIG. 8 is a plot of the coercivity (H_(c)) versus media grain pitch forvarious quad exchange coupling layer (ECL) structures having differentG0 thicknesses. As used herein in various embodiments, a quad ECLstructure refers to a perpendicular magnetic recording medium having amagnetic recording layer structure with four exchange coupling layersand five magnetic recording layers; whereas, a triple ECL structurerefers to a perpendicular magnetic recording medium having a magneticrecording layer structure with three exchange coupling layers and fourmagnetic recording layers. As also used herein in various embodiments,the G0 layer corresponds to the lowermost magnetic recording layer in aquad ECL structure, whereas the G1 layer corresponds to the lowermostmagnetic recording layer in a triple ECL structure.

FIG. 9 is a plot of the nucleation field (H_(n)) versus media grainpitch for various quad ECL structures having different G0 thicknesses.

FIG. 10 is a plot of the switching field distribution (SFD) versus mediagrain pitch for various quad ECL structures having different G0thicknesses.

FIG. 11 is a plot of the thermal stability (K_(u)V/k_(B)T) versus mediagrain pitch for various quad ECL structures having different G0thicknesses.

FIG. 12 is a plot of the intrinsic switching field distribution (iSFD)versus media grain pitch for various quad ECL structures havingdifferent G0 thicknesses.

FIG. 13 is a plot of the magnetic cluster size versus media grain pitchfor various quad ECL structures having different G0 thicknesses.

FIG. 14 is a plot of the overwrite (OW) versus media grain pitch for atriple ECL structure and various quad ECL structures with different G0thicknesses.

FIG. 15 is a plot of magnetic core width (MCW) versus media grain pitchfor a triple ECL structure and various quad ECL structures withdifferent G0 thicknesses.

FIG. 16 is a plot of 6 TSoNR versus media grain pitch for a triple ECLstructure and various quad ECL structures with different G0 thicknesses.

FIG. 17 is a plot of 2 TSoNR versus media grain pitch for a triple ECLstructure and various quad ECL structures with different G0 thicknesses.

FIG. 18 is a plot of 1 TSoNR versus media grain pitch for a triple ECLstructure and various quad ECL structures with different G0 thicknesses.

FIG. 19 is a plot of 2 TSoNR versus 6 TMCW for a triple ECL structureand various quad ECL structures with different G0 thicknesses.

FIG. 20 is a plot of 1 TSoNR versus 6 TMCW for a triple ECL structureand various quad ECL structures with different G0 thicknesses.

FIG. 21 is a plot of 2 TSoNR versus 6 TMCW for two triple ECL structuresand quad ECL structure.

FIG. 22 is a plot of 1 TSoNR versus 6 TMCW for two triple ECL structuresand quad ECL structure.

FIG. 23 is a plot of OW versus G0 thickness for a triple ECL structureand various quad ECL structures having different exchange break layer(EBL) structure thicknesses.

FIG. 24 is a plot of OW versus overall thickness of the soft magneticunderlay (SUL) structure for two quad ECL structures and a triple ECLstructure.

FIG. 25 is a plot of MCW versus overall thickness of the soft magneticunderlay (SUL) structure for two quad ECL structures and a triple ECLstructure.

FIG. 26 is a plot of 2 TSoNR versus overall thickness of the softmagnetic underlay (SUL) structure for two quad ECL structures and atriple ECL structure.

FIG. 27 is a plot of 1 TSoNR versus overall thickness of the softmagnetic underlay (SUL) structure for two quad ECL structures and atriple ECL structure.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems and/or related systems and methods, as well asoperation and/or component parts thereof.

In one general embodiment, a magnetic recording medium includes: asubstrate; and a magnetic recording layer structure formed above thesubstrate. The magnetic recording layer structure includes: a firstrecording magnetic layer having a first magnetic anisotropy field(H_(k)) value greater than or equal to about 20 kOe; a first nonmagneticexchange coupling layer formed above the first magnetic recording layer;a second magnetic recording layer formed above the first nonmagneticexchange coupling layer, the second magnetic recording layer having asecond H_(k) value that is less than or about equal to the first H_(k)value of the first magnetic recording layer; a second nonmagneticexchange coupling layer formed above the second magnetic recordinglayer; a third magnetic recording layer formed above the secondnonmagnetic exchange coupling layer, the third magnetic recording layerhaving a third H_(k) value that is less than or about equal to the firstH_(k) value of the first magnetic recording layer; a third nonmagneticexchange coupling layer formed above the third magnetic recording layer;a fourth magnetic recording layer formed above the third nonmagneticexchange coupling layer, the fourth magnetic recording layer having afourth H_(k) value that is less than or about equal to the first H_(k)value of the first magnetic recording layer; a fourth nonmagneticexchange coupling layer formed above the fourth magnetic recordinglayer; and a fifth magnetic recording layer formed above the fourthnonmagnetic exchange coupling layer, the fifth magnetic recording layerhaving a fifth H_(k) value that is less than or about equal to the firstH_(k) value of the first magnetic recording layer.

In another general embodiment, a magnetic recording medium includes: asubstrate; and a magnetic recording layer structure formed above thesubstrate. The magnetic recording layer structure includes five or moremagnetic recording layers and four or more nonmagnetic exchange couplinglayers, where the magnetic recording layers and the nonmagnetic exchangecoupling layers are arranged in an alternating pattern, and where themagnetic recording layers are separated from each other by least one ofthe nonmagnetic exchange coupling layers. The magnetic recording layerpositioned closest to the substrate has each of the following: anaverage magnetic grain pitch of about 8.3 nm or less, a magneticanisotropy field (H_(k)) value of greater than or equal to about 20 kOe,and a thickness that is about 40% of a total thickness of the magneticrecording layer structure.

Referring now to FIG. 1, there is shown a disk drive 100 in accordancewith one embodiment of the present invention. As shown in FIG. 1, atleast one rotatable magnetic medium (e.g., magnetic disk) 112 issupported on a spindle 114 and rotated by a drive mechanism, which mayinclude a disk drive motor 118. The magnetic recording on each disk istypically in the form of an annular pattern of concentric data tracks(not shown) on the disk 112. The disk drive motor 118 preferably passesthe magnetic disk 112 over the magnetic read/write portions 121,described immediately below.

At least one slider 113 is positioned near the disk 112, each slider 113supporting one or more magnetic read/write portions 121, e.g., of amagnetic head according to any of the approaches described and/orsuggested herein. As the disk rotates, slider 113 is moved radially inand out over disk surface 122 so that portions 121 may access differenttracks of the disk where desired data are recorded and/or to be written.Each slider 113 is attached to an actuator arm 119 by means of asuspension 115. The suspension 115 provides a slight spring force whichbiases slider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator 127. The actuator 127 as shown in FIG. 1 may bea voice coil motor (VCM). The VCM comprises a coil movable within afixed magnetic field, the direction and speed of the coil movementsbeing controlled by the motor current signals supplied by controller129.

During operation of the disk storage system, the rotation of disk 112generates an air bearing between slider 113 and disk surface 122 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 115 and supportsslider 113 off and slightly above the disk surface by a small,substantially constant spacing during normal operation. Note that insome embodiments, the slider 113 may slide along the disk surface 122.

The various components of the disk storage system are controlled inoperation by control signals generated by controller 129, such as accesscontrol signals and internal clock signals. Typically, control unit 129comprises logic control circuits, storage (e.g., memory), and amicroprocessor. In a preferred approach, the control unit 129 iselectrically coupled (e.g., via wire, cable, line, etc.) to the one ormore magnetic read/write portions 121, for controlling operationthereof. The control unit 129 generates control signals to controlvarious system operations such as drive motor control signals on line123 and head position and seek control signals on line 128. The controlsignals on line 128 provide the desired current profiles to optimallymove and position slider 113 to the desired data track on disk 112. Readand write signals are communicated to and from read/write portions 121by way of recording channel 125.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 1 is for representation purposes only.It should be apparent that disk storage systems may contain a largenumber of disks and actuators, and each actuator may support a number ofsliders.

An interface may also be provided for communication between the diskdrive and a host (integral or external) to send and receive the data andfor controlling the operation of the disk drive and communicating thestatus of the disk drive to the host, all as will be understood by thoseof skill in the art.

In a typical head, an inductive write portion includes a coil layerembedded in one or more insulation layers (insulation stack), theinsulation stack being located between first and second pole piecelayers. A gap is formed between the first and second pole piece layersby a gap layer at an air bearing surface (ABS) of the write portion. Thepole piece layers may be connected at a back gap. Currents are conductedthrough the coil layer, which produce magnetic fields in the polepieces. The magnetic fields fringe across the gap at the ABS for thepurpose of writing bits of magnetic field information in tracks onmoving media, such as in circular tracks on a rotating magnetic disk.

The second pole piece layer has a pole tip portion which extends fromthe ABS to a flare point and a yoke portion which extends from the flarepoint to the back gap. The flare point is where the second pole piecebegins to widen (flare) to form the yoke. The placement of the flarepoint directly affects the magnitude of the magnetic field produced towrite information on the recording medium.

FIG. 2A is a cross-sectional view of a perpendicular magnetic head 200,according to one embodiment. In FIG. 2A, helical coils 210 and 212 areused to create magnetic flux in the stitch pole 208, which then deliversthat flux to the main pole 206. Coils 210 indicate coils extending outfrom the page, while coils 212 indicate coils extending into the page.Stitch pole 208 may be recessed from the ABS 218. Insulation 216surrounds the coils and may provide support for some of the elements.The direction of the media travel, as indicated by the arrow to theright of the structure, moves the media past the lower return pole 214first, then past the stitch pole 208, main pole 206, trailing shield 204which may be connected to the wrap around shield (not shown), andfinally past the upper return pole 202. Each of these components mayhave a portion in contact with the ABS 218. The ABS 218 is indicatedacross the right side of the structure.

Perpendicular writing is achieved by forcing flux through the stitchpole 208 into the main pole 206 and then to the surface of the diskpositioned towards the ABS 218.

FIG. 2B illustrates one embodiment of a piggyback magnetic head 201having similar features to the head 200 of FIG. 2A. As shown in FIG. 2B,two shields 204, 214 flank the stitch pole 208 and main pole 206. Alsosensor shields 222, 224 are shown. The sensor 226 is typicallypositioned between the sensor shields 222, 224.

FIG. 3A is a schematic diagram of another embodiment of a perpendicularmagnetic head 300, which uses looped coils 310 to provide flux to thestitch pole 308, a configuration that is sometimes referred to as apancake configuration. The stitch pole 308 provides the flux to the mainpole 306. With this arrangement, the lower return pole may be optional.Insulation 316 surrounds the coils 310, and may provide support for thestitch pole 308 and main pole 306. The stitch pole may be recessed fromthe ABS 318. The direction of the media travel, as indicated by thearrow to the right of the structure, moves the media past the stitchpole 308, main pole 306, trailing shield 304 which may be connected tothe wrap around shield (not shown), and finally past the upper returnpole 302 (all of which may or may not have a portion in contact with theABS 318). The ABS 318 is indicated across the right side of thestructure. The trailing shield 304 may be in contact with the main pole306 in some embodiments.

FIG. 3B illustrates another embodiment of a piggyback magnetic head 301having similar features to the head 300 of FIG. 3A. As shown in FIG. 3B,the piggyback magnetic head 301 also includes a looped coil 310, whichwraps around to form a pancake coil. Sensor shields 322, 324 areadditionally shown. The sensor 326 is typically positioned between thesensor shields 322, 324.

In FIGS. 2B and 3B, an optional heater is shown near the non-ABS side ofthe magnetic head. A heater (Heater) may also be included in themagnetic heads shown in FIGS. 2A and 3A. The position of this heater mayvary based on design parameters such as where the protrusion is desired,coefficients of thermal expansion of the surrounding layers, etc.

FIG. 4 provides a schematic diagram of a simplified perpendicularrecording medium 400, which may also be used with magnetic diskrecording systems, such as that shown in FIG. 1. As shown in FIG. 4, theperpendicular recording medium 400, which may be a recording disk invarious approaches, comprises at least a supporting substrate 402 of asuitable non-magnetic material (e.g., glass, aluminum, etc.), and a softmagnetic underlayer 404 of a material having a high magneticpermeability positioned above the substrate 402. The perpendicularrecording medium 400 also includes a magnetic recording layer 406positioned above the soft magnetic underlayer 404, where the magneticrecording layer 406 preferably has a high coercivity relative to thesoft magnetic underlayer 404. There may one or more additional layers(not shown), such as an “exchange-break” layer or “interlayer”, betweenthe soft magnetic underlayer 404 and the magnetic recording layer 406.

The orientation of magnetic impulses in the magnetic recording layer 406is substantially perpendicular to the surface of the recording layer.The magnetization of the soft magnetic underlayer 404 is oriented in (orparallel to) the plane of the soft underlayer 404. As particularly shownin FIG. 4, the in-plane magnetization of the soft magnetic underlayer404 may be represented by an arrow extending into the paper.

FIG. 5A illustrates the operative relationship between a perpendicularhead 508 and the perpendicular recording medium 400 of FIG. 4. As shownin FIG. 5A, the magnetic flux 510, which extends between the main pole512 and return pole 514 of the perpendicular head 508, loops into andout of the magnetic recording layer 406 and soft magnetic underlayer404. The soft magnetic underlayer 404 helps focus the magnetic flux 510from the perpendicular head 508 into the magnetic recording layer 406 ina direction generally perpendicular to the surface of the magneticmedium. Accordingly, the intense magnetic field generated between theperpendicular head 508 and the soft magnetic underlayer 404, enablesinformation to be recorded in the magnetic recording layer 406. Themagnetic flux is further channeled by the soft magnetic underlayer 404back to the return pole 514 of the head 508.

As noted above, the magnetization of the soft magnetic underlayer 404 isoriented in (parallel to) the plane of the soft magnetic underlayer 404,and may represented by an arrow extending into the paper. However, asshown in FIG. 5A, this in plane magnetization of the soft magneticunderlayer 404 may rotate in regions that are exposed to the magneticflux 510.

FIG. 5B illustrates one embodiment of the structure shown in FIG. 5A,where soft magnetic underlayers 404 and magnetic recording layers 406are positioned on opposite sides of the substrate 402, along withsuitable recording heads 508 positioned adjacent the outer surface ofthe magnetic recording layers 406, thereby allowing recording on eachside of the medium.

Except as otherwise described herein with reference to the variousinventive embodiments, the various components of the structures of FIGS.1-5B, and of other embodiments disclosed herein, may be of conventionalmaterial(s), design, and/or fabricated using conventional techniques, aswould become apparent to one skilled in the art upon reading the presentdisclosure.

Referring now to FIG. 6, a perpendicular magnetic recording medium 600comprising a recording layer structure having three exchange couplinglayers is shown according to one embodiment. As an option, theperpendicular magnetic recording medium 600 may be implemented inconjunction with features from any other embodiment listed herein, suchas those described with reference to the other FIGS. Of course, theperpendicular magnetic recording medium 600 and others presented hereinmay be used in various applications and/or in permutations which may ormay not be specifically described in the illustrative embodiments listedherein. For instance, the perpendicular magnetic recording medium 600may include more or less layers than those shown in FIG. 6, in variousapproaches. Moreover, unless otherwise specified, formation of one ormore of the layers shown in FIG. 6 may be achieved via atomic layerdeposition (ALD), chemical vapor deposition (CVD), evaporation, e-beamevaporation, ion beam deposition, sputtering, or other depositiontechnique as would become apparent to a skilled artisan upon reading thepresent disclosure. Further, the perpendicular magnetic recording medium600 and others presented herein may be used in any desired environment.

As shown in FIG. 6, the perpendicular magnetic recording medium 600includes a substrate 602 comprising a material of high rigidity, such asglass, Al, Al₂O₃, AlMg, MgO, Si, or other suitable substrate material aswould be understood by one having skill in the art upon reading thepresent disclosure. In some approaches, the substrate 602 may have athickness that is greater than or less than the other layers formedthereon.

The perpendicular magnetic recording medium 600 also includes anadhesion layer 604 formed above the substrate 602, the adhesion layer604 being configured to improve adhesion between the substrate 602 andthe layers deposited thereon. The adhesion layer 604 may also beconfigured to control the size of the magnetic grains in one or more ofthe layers of the magnetic recording layer structure 624. In preferredapproaches, the adhesion layer 604 comprises an amorphous material thatdoes not affect the crystal orientation of the layers deposited thereon.Suitable materials for the adhesion layer 604 include, but are notlimited to, Ni, Co, Al, Ti, Cr, Zr, Ta, Nb and combinations and/oralloys thereof.

The perpendicular magnetic recording medium 600 additionally includes asoft magnetic underlayer structure 606 formed above the adhesion layer604, the soft magnetic underlayer structure 606 being configured topromote data recording in one or more of the magnetic recording layersof the magnetic recording layer structure 624 by suppressing the spreadof the magnetic field and efficiently magnetizing the one or moremagnetic recording layers. As shown in FIG. 6, the soft magneticunderlayer structure 606 includes a first soft magnetic underlayer 608and a second soft magnetic underlayer 612 separated by ananti-ferromagnetic coupling (AFC) layer 610, typically of Ru or otherAFC material as known in the art. The first and second soft magneticunderlayers 608, 612 may each independently be comprised of cobalt,iron, tantalum, zirconium, nickel, boron, chromium, or compositionsthereof, etc., which preferably provide a high moment.

An exchange break layer structure 614 is formed above the soft magneticunderlayer structure 606, the exchange break layer structure 614 beingconfigured to control the grain size and crystalline orientation of thelayers formed thereabove, as well as magnetically decouple themagnetically permeable layers of the soft magnetic underlayer structure606 and the magnetic recording layers of the magnetic recording layerstructure 624. As shown in FIG. 6, the exchange break layer structure614 includes a first exchange break layer 616, also referred to hereinas a seed layer. The first exchange break layer 616 may include at leastone of Ni, Cu, Pd, Pt, Cr, W, V, Mo, Ta, Nb, Fe, and other suitablematerials as would become apparent to one skilled in the art uponreading the present disclosure.

The exchange break layer structure 614 also includes a second exchangebreak layer 618 formed above the first exchange break layer 616, and athird exchange break layer 620 formed above the second exchange breaklayer 618, where the second and third exchange break layers may also bereferred to herein as underlayers. The second and third exchange breaklayers 618, 620 may include one or more materials having a hexagonalclose packed (hcp) crystalline structure, such as Ru, or other suchsuitable material as would become apparent to one having skill in theart upon reading the present disclosure. In various approaches, thesecond and third exchange break layers 618, 620 may be formed underdifferent gas pressures during sputtering, such as a lower pressure forthe second exchange break layer 618, and higher pressures for the thirdexchange break layer 620.

The exchange break layer structure 614 further includes a fourthexchange break layer 622, which may be referred to herein as an onsetlayer, formed above the third exchange break layer 620. Suitablematerials for the fourth exchange break layer 622 may include ruthenium,titanium, tantalum, and/or oxides thereof, etc.

As shown in FIG. 6, the magnetic recording layer structure 624 is formedabove the exchange break layer structure 614, the magnetic recordinglayer structure 624 having four magnetic recording layers 626, 630, 634,638 and three exchange coupling layers 628, 632, 636. In the embodimentdepicted in FIG. 6, the magnetic recording layer structure 624 includesan alternating pattern of magnetic recording layers and exchangecoupling layers. For instance, the magnetic recording layer structure624 includes the first magnetic recording layer 626, the first exchangecoupling layer 628 formed above the first magnetic recording layer 626,the second magnetic recording layer 630 formed above the first exchangecoupling layer 628, the second exchange coupling layer 632 formed abovethe second magnetic recording layer 630, the third magnetic recordinglayer 634 formed above the second exchange coupling layer 632, the thirdexchange coupling layer 636 formed above the third magnetic recordinglayer 634, and the fourth magnetic recording layer 638 (also referred toas the cap layer 638) formed above the third exchange coupling layer636.

The three lowermost magnetic recording layers 626, 630, 634 in themagnetic recording layer structure 624 each include a plurality ofgrains separated from one another via a segregant material. Illustrativematerials for one or more of the magnetic recording layers 626, 630, 634may include CoCrPtX+oxide and/or O₂, where X denotes one or moreoptional alloying elements such as B, Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo,Mn, etc., and where the oxide may be TiO_(x), SiO_(x), B₂O₃, W₂O₅,Ta₂O₅, NbO₂, CoO, Co₃O₄, etc.

The thickness of the first magnetic recording layer 626 may typically bein a range from 4 nm to 5.5 nm. It has been found that for magneticrecording layer structures having four magnetic recording layers andthree exchange coupling layers, such as the magnetic recording layerstructure 624 shown in FIG. 6, increasing the thickness of the lowermostmagnetic recording layer (see e.g., the first magnetic recording layer626) above 5.5 nm substantially reduces or completely precludes mediawriteability.

With continued reference to FIG. 6, the thicknesses of the second andthird magnetic recording layers 630, 634 may each independently be in arange from 0.5 nm to about 3 nm in various approaches. In someapproaches, the second and third magnetic recording layers 630, 634 mayhave a thickness that is the same or different from one another. In oneparticular approach, the thickness of the second magnetic recordinglayer 630 may be about 2.8 nm, and the thickness of the third magneticrecording layer 634 may be about 1.2 nm.

In various approaches, the magnetic anisotropy, K_(u), of the firstmagnetic recording layer 626 may be greater than the K_(u) of the secondmagnetic recording layer 630. In more approaches, the magneticanisotropy, K_(u), of the first magnetic recording layer 626 may begreater than the K_(u) of the second magnetic recording layer 630 andthe K_(u) of the third magnetic recording layer 634. In yet moreapproaches where the K_(u) values of the first and third magneticrecording layers 626, 634 are greater than the K_(u) of the secondmagnetic recording layer 630, the K_(u) of the first magnetic recordinglayer 626 may be greater than or about equal to the K_(u) of the thirdmagnetic recording layer 634.

As noted previously, the magnetic recording layer structure 624 includesthree exchange coupling layers 628, 632, 636 configured to magneticallydecouple the magnetic recording layers 626, 630, 634, 638, as well aspromote the grain growth and crystalline orientation of the layersformed thereabove. Each of the exchange coupling layers 628, 632, 636may include a plurality of grains separated from one another via asegregant material. Moreover, each of the exchange coupling layers 628,632, 636 are preferably nonmagnetic.

In preferred approaches, one or more of the exchange coupling layers628, 632, 636 may include one or more of the same materials as one ormore of the magnetic recording layers 626, 630, 634, though notnecessarily in the same stoichiometric proportions given that theexchange coupling layers 628, 632, 636 are preferably nonmagnetic. Forinstance, in one preferred approach, one or more of the exchangecoupling layers 628, 632, 636 may include CoCrPtX+oxide and/or O, whereX denotes one or more optional alloying elements such as B, Ta, Si, Ru,Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may be TiO_(x),SiO_(x), B₂O₃, W₂O₅, Ta₂O₅, NbO₂, CoO, Co₃O₄, etc.

In various approaches, the thicknesses of the exchange coupling layers628, 632, 636, may each independently be in a range from 0.5 nm to 2 nm.In some approaches, some or all of the exchange coupling layers 628,632, 636 may have thicknesses that are the same or different relative toone another.

As additionally shown in FIG. 6, the fourth magnetic recording layer638, also referred to as a cap layer, is the uppermost layer in themagnetic recording layer structure 624. Suitable materials for the caplayer 638 may include, but are not limited to, a Co—, CoCr—, CoPtCr—,and/or CoPtCrB— based alloy, or other such material as would becomeapparent to one having skill in the art upon reading the presentdisclosure. In various approaches, the cap layer 638 may be a continuouscap layer. In some approaches, the cap layer 638 may be a continuous,partially oxidized cap layer formed by flowing a mixture of oxygen andargon to distribute the oxygen in the cap layer. In particularapproaches, the cap layer 638 may be formed at a lower argon pressurethan all other magnetic recording layers positioned therebelow, thusforming a cap layer that is continuous, or at least more continuous thanall other magnetic recording layers in the magnetic recording layerstructure 624.

As also shown in FIG. 6, a protective overcoat layer 640 is formed abovethe cap layer 638. Suitable materials for the overcoat layer 640 mayinclude, but are not limited to, diamond-like carbon, carbon nitride,Si-nitride, BN or B4C, etc.

An optional lubricant layer (not shown in FIG. 6) may be formed abovethe protective overcoat layer 640. Suitable materials for the optionallubricant layer may also include, but are not limited to,perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acids,etc.

As noted previously, efforts are continually made to increase the arealrecording density of magnetic media. Areal density, e.g., as measured inbits per square inch, may be defined as the product of the track density(the tracks per inch radially on the magnetic medium, such as a disk)and the linear density (the bits per inch along each track). For a disk,the bits are written closely-spaced to form circular tracks on the disksurface, where each of the bits may comprise an ensemble of magneticgrains.

An important factor relevant to track density is the magnetic core width(MCW). The magnetic core width corresponds to the width of a magneticbit recorded by the write pole of the write head. Thus, the smaller themagnetic core width, the greater the number of tracks of data that canbe written to the media. Stated another way, high track density isassociated with a narrow magnetic core width.

Moreover, an important factor relevant to linear density is the signalto noise ratio (SNR). Typically, a higher signal to noise ratiocorresponds to a higher readable linear density. One approach toincrease the signal to noise ratio involves reducing the size of themagnetic grains included within a magnetic recording layer. Forinstance, to support an areal density of 1 Tbit/in2 or more, themagnetic grain size needs to be reduced down to about an 8 nm pitchlevel. However, reducing the size of the magnetic grains may affecttheir thermal stability, represented as: K_(u)V/k_(B)T, where K_(u)denotes the magnetocrystalline anisotropy, V is the average grainvolume, k_(B) denotes the Boltzmann constant, and T denotes the absolutetemperature. To avoid thermal decay, K_(u)V/k_(B)T should be greaterthan or equal to about 60, and is preferably greater than or equal toabout 80.

To compensate for the reduction in volume, V, of the magnetic grains,the magnetic anisotropy (K_(u)) of the magnetic grains may be increasedto maintain thermal stability. For instance, in one approach, a highK_(u) portion of a magnetic recording layer structure, which maytypically be the lowermost portion of the magnetic recording layerstructure (see e.g., the high K_(u) magnetic recording layer 626 shownin FIG. 6), may be increased (e.g., the thickness of the high K_(u)portion may be increased) to maintain thermal stability of the magneticgrains therein. However, such an increase in this high K_(u) portion ofa magnetic recording layer structure may decrease the media writeability(i.e., the ease at which information may be recording in the magneticmaterial).

Various embodiments disclosed herein overcome such drawbacks byproviding perpendicular magnetic storage media comprising novel magneticrecording layer structures having at least five magnetic recordinglayers and at least four exchange coupling layers. In preferredapproaches, the lowermost magnetic recording layer in these novelmagnetic recording layer structures has a high magnetic anisotropy(e.g., a magnetic anisotropy field, H_(k), greater than or equal toabout 20 kOe), a film thickness greater than or equal to about 6 nm,preferably in a range from about 6 nm to about 8 nm, and an averagegrain pitch of about 8.3 nm or less, thus leading to small, yetthermally stable magnetic grains. Moreover, it has been surprisingly andunexpectedly found that these novel magnetic recording layer structureshaving at least five magnetic recording layers and at least fourexchange coupling layers exhibit improved magnetic recordingcharacteristics (e.g., signal-to-noise ratio (SNR), overwrite (OW),magnetic core width (MCW), etc.) as compared to magnetic recording layerstructures having no more than four magnetic recording layers and nomore than three exchange coupling layers (e.g., as shown in FIG. 6). Thesuperior magnetic recording characteristics, such as the OW, exhibitedby these novel magnetic recording layer structures is indeed surprisingand unexpected given the overall increase in the thickness of saidmagnetic recording layer structures (e.g., via addition of at least oneadditional magnetic recording layer and at least one additional exchangecoupling layer, and incorporation of a thick, high K_(u) lowermostmagnetic recording layer).

In more approaches, superior magnetic recording characteristics (e.g.,SNR, OW, MCW, etc.) may also be achieved in approaches where these novelmagnetic recording structures, e.g., those having at least five magneticrecording layers and at least four exchange coupling layers, are formedabove an antiferromagnetically-coupled soft magnetic underlayerstructure having a thickness less than or equal to about 35 nm,preferably less than or equal to about 25 nm. In yet more approaches,superior magnetic recording characteristics may additionally be achievedin approaches where these novel magnetic recording structures are formedabove, and preferably directly on, an exchange break layer structurehaving a thickness less than or equal to about 15 nm.

Referring now to FIGS. 7A-7B, perpendicular magnetic recording media700, 701 each comprising a recording layer structure having at leastfour exchange coupling layers are shown according to one embodiment. Asan option, the perpendicular magnetic recording media 700, 701 may beimplemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the other FIGS.Of course, the perpendicular magnetic recording media 700, 701 andothers presented herein may be used in various applications and/or inpermutations which may or may not be specifically described in theillustrative embodiments listed herein. For instance, the perpendicularmagnetic recording media 700, 701 may include more or less layers thanthose shown in FIGS. 7A-7B, in various approaches. Moreover, unlessotherwise specified, formation of one or more of the layers shown inFIGS. 7A-7B may be achieved via atomic layer deposition (ALD), chemicalvapor deposition (CVD), evaporation, e-beam evaporation, ion beamdeposition, sputtering, or other deposition technique as would becomeapparent to a skilled artisan upon reading the present disclosure.Further, the perpendicular magnetic recording media 700, 701 and otherspresented herein may be used in any desired environment.

As shown in FIG. 7A, the perpendicular magnetic recording medium 700includes a substrate 702 comprising a material of high rigidity, such asglass, Al, Al₂O₃, AlMg, MgO, Si, or other suitable substrate material aswould be understood by one having skill in the art upon reading thepresent disclosure. In some approaches, the substrate 702 may have athickness that is greater than or less than the other layers formedthereon.

The perpendicular magnetic recording medium 700 also includes anadhesion layer 704 formed above the substrate 702. The adhesion layer704 is configured to improve adhesion between the substrate 702 and thelayers deposited thereon. The adhesion layer 704 may also be configuredto control the size of the magnetic grains in one or more of the layersof the magnetic recording layer structure 724. In preferred approaches,the adhesion layer 704 comprises an amorphous material that does notaffect the crystal orientation of the layers deposited thereon. Suitablematerials for the adhesion layer 704 include, but are not limited to,Ni, Co, Al, Ti, Cr, Zr, Ta, Nb and combinations and/or alloys thereof.In particular approaches, the adhesion layer 704 may include at leastone of TiAl, NiTa, TiCr, AlCr, NiTaZr, CoNbZr, TiAlCr, NiAlTi, CoAlTi,etc., or other suitable material as would become apparent to one havingskill in the art upon reading the present disclosure. In moreapproaches, a thickness of the adhesion layer 704 may be in a range fromabout 1 nm to about 30 nm; however, as with any range pertaining tofeatures shown in FIGS. 7A-7B, the upper and lower values could behigher or lower in various other approaches. In one preferred approach,the thickness of the adhesion layer 704 may be about 1.5 nm.

The perpendicular magnetic recording medium 700 additionally includes asoft magnetic underlayer structure 706. The soft magnetic underlayerstructure 706 is configured to promote data recording in one or more ofthe magnetic recording layers of the magnetic recording layer structure724 by suppressing the spread of the magnetic field and efficientlymagnetizing the one or more magnetic recording layers. As shown in FIG.7A, the soft magnetic underlayer structure 706 includes a coupling layer710 sandwiched between a first soft magnetic underlayer 708 and a secondsoft magnetic underlayer 712, where the coupling layer 710 is configuredto induce an anti-ferromagnetic coupling between the first and secondsoft magnetic underlayers 708, 712.

In various approaches, the first and/or second soft magnetic underlayers708, 712 include one or more materials having a high magneticpermeability. Accordingly, suitable materials for the first and/or thesecond soft magnetic underlayers 708, 712 include, but are not limitedto, amorphous alloys including Co and/or Fe as the main component(s),with at least one of: Ta, Hf, Nb, Si, Zr, B, C, Cr, Ni, etc. addedthereto. Illustrative examples of suitable materials for the firstand/or the second soft magnetic underlayers 708, 712 may include CoNiFe,FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoTaZr, CoFeTa,CoFeTaZr, CoFeB, CoZrNb, etc. Suitable materials for the coupling layer710 include at least one of Ru, Ir, Cr, and other anti-ferromagneticcoupling materials as would become apparent to one skilled in the artupon reading the present disclosure.

The optimum thickness of the soft magnetic underlayer (SUL) structure706 may depend on the material(s) of the first and second soft magneticunderlayers 708, 712 and/or the coupling layer 710, the structure andmaterial(s) of the magnetic head configured to apply a magnetic field tothe perpendicular magnetic recording medium 700, and/or the distancebetween the soft magnetic underlayer structure 706 and the magneticrecording layer structure 724, in various approaches. However, in someapproaches, a total thickness, t_(sul), of the soft magnetic underlayerstructure 706 may be in a range from about 10 nm to about 50 nm,preferably in a range from about 12 nm to about 35 nm, even morepreferably in a range from about 12 nm to about 15 nm. In moreapproaches, a thickness of the first soft magnetic underlayer 708 may bein a range from about 5 nm to about 25 nm. In yet more approaches, athickness of the second soft magnetic underlayer 712 may be in a rangefrom about 5 nm to about 25 nm. In still more approaches, a thickness ofthe coupling layer 710 may be in a range from about 0.5 nm to about 2nm.

As further shown in FIG. 7A, the perpendicular magnetic recording medium700 includes an exchange break layer (EBL) structure 714 positionedabove the soft magnetic underlayer structure 706. The exchange breaklayer structure 714 is configured to magnetically decouple themagnetically permeable layers of the soft magnetic underlayer structure706 and the magnetic recording layers of the magnetic recording layerstructure 724. The exchange break layer structure 714 is also configuredto control the grain size and crystalline orientation of the layersformed thereabove.

In various approaches, the exchange break layer structure 714 mayinclude one or more layers. For example, in the embodiment depicted inFIG. 7A, the exchange break layer structure 714 may include at leastfour separate exchange break layers. In various approaches, a totalthickness, t_(ebl), of the exchange break layer structure 714 may beless than or equal to about 15 nm.

The first exchange break layer 716, also referred to herein as the seedlayer, is configured to control the size of the magnetic grains in oneor more of the layers of the magnetic recording layer structure 724. Insome approaches, the first exchange break layer 716 may include one ormore nonmagnetic materials having a face centered cubic (fcc)crystalline structure. In particular approaches, the first exchangebreak layer 716 may include at least one of Ni, Cu, Pd, Pt, Cr, W, V,Mo, Ta, Nb, Fe, and other suitable materials as would become apparent toone skilled in the art upon reading the present disclosure. In moreapproaches, the first exchange break layer 716 may not include an oxide.In further approaches, the first exchange break layer 716 may have athickness in a range from about 2 nm to about 8 nm.

The exchange break layer structure 714 also includes a second exchangebreak layer 718 formed above the first exchange break layer 716, and athird exchange break layer 720 formed above the second exchange breaklayer 718, where the second and third exchange break layers may also bereferred to herein as underlayers. In various approaches, the secondand/or third exchange break layers 718, 720 may be configured to controlthe crystalline orientation of the layers formed thereabove,particularly one or more of the layers of the magnetic recording layerstructure 724. For instance, in one particular approach, the secondand/or third exchange break layers 718, 720 may include one or morematerials having a hexagonal close packed (hcp) crystalline structurethat promotes the epitaxial growth of one or more of the layers of themagnetic recording layer structure 724 such that the c-axis of saidlayers is oriented substantially perpendicular to the upper surfacethereof, thus resulting in perpendicular magnetic anisotropy.

In a preferred approach, the second and/or third exchange break layers718, 720 may include Ru. In an even more preferred approach, the secondand third exchange break layers 718, 720 may include Ru formed underdifferent gas pressures during sputtering, e.g., a lower pressure forthe second exchange break layer 718, and a higher pressure for the thirdexchange break layer 720. In additional approaches, the second and/orthird exchange break layers 718, 720 may include Ru and a small amountof one or more of Ti, Ta, B, Cr or Si.

In more approaches, a thickness of the second and/or third exchangebreak layers 718, 720 may be in a range from about 3 nm to about 10 nm.

The exchange break layer structure 714 additionally includes a fourthexchange break layer 722 formed above the third exchange break layer720. The fourth exchange break layer 722 may also be referred to hereinas an onset layer. In various approaches, the fourth exchange breaklayer 722 may be configured to control the crystalline orientationand/or to promote the separation of the magnetic grains in one or morelayers of the magnetic recording layer structure 724. In someapproaches, the fourth exchange break layer 722 may also include one ormore materials having a hexagonal close packed (hcp) crystallinestructure, such as Ru. In preferred approaches, the fourth exchangebreak layer 722 may include Ru and at least one oxide, such as TiO₂,Ti₂O₅, WO₃, W₂O₅, Ta₂O₅, SiO₂, B₂O₃, etc. In more approaches, the fourthexchange break layer 722 may include Ru, at least one oxide, and a smallamount of one or more of Ti, Ta, B, Cr and Si.

In further approaches, a thickness of the fourth exchange break layer722 may be in a range from about 0.5 nm to about 2.0 nm. In numerousapproaches, the fourth exchange break layer 722 may be substantiallythinner than the second and/or third exchange break layers 718, 720.

As shown in FIG. 7A, the perpendicular magnetic recording medium 700includes a magnetic recording layer structure 724 formed above theexchange break layer structure 714. In various approaches, the magneticrecording layer structure 724 may include one or more magnetic recordinglayers and one or more exchange coupling layers. For example, in theembodiment depicted in FIG. 7A, the magnetic recording layer structure724 may include at least five magnetic recording layers 726, 730, 734,738, 744, and at least four exchange coupling layers 728, 732, 736, 740.In such an embodiment, the magnetic recording layer structure 724includes an alternating pattern of magnetic recording layers andexchange coupling layers. As particularly shown in FIG. 7A, the magneticrecording layer structure 724 includes the first magnetic recordinglayer 726, the first exchange coupling layer 728 formed above the firstmagnetic recording layer 726, the second magnetic recording layer 730formed above the first exchange coupling layer 728, the second exchangecoupling layer 732 formed above the second magnetic recording layer 730,the third magnetic recording layer 734 formed above the second exchangecoupling layer 732, the third exchange coupling layer 736 formed abovethe third magnetic recording layer 734, the fourth magnetic recordinglayer 738 formed above the third exchange coupling layer 736, the fourthexchange coupling layer 740 formed above the fourth magnetic recordinglayer 738, and the fifth magnetic recording layer 744 (also referred toas the cap layer 744) formed above the fourth exchange coupling layer740.

In some approaches, a total thickness, t_(mrl), of the magneticrecording layer structure 724 may be in a range from about 12 nm toabout 20 nm. In more approaches, the magnetic recording layer structure724 has a thermal stability factor (K_(u)V/k_(B)T) of greater than orequal to about 80.

The four lowermost magnetic recording layers 726, 730, 734, 738 in themagnetic recording layer structure 724 may each include a plurality ofgrains separated from one another via a segregant material. In variousapproaches, the grains of one or more of the magnetic recording layers726, 730, 734, 738 may include one or more of Co, Cr, Fe, Ta, Ni, Mo,Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, Pd. In more approaches, thesegregant material of one or more of the magnetic recording layers 726,730, 734, 738 may include O and/or at least one oxide of Ta, W, Nb, VMo, B, Si, Co, Cr, Ti, or Al. In one particular approach, one or more ofthe magnetic recording layers 726, 730, 734, 738 may includeCoCrPtX+oxide and/or O, where X may be B, Ta, Si, Ru, Ti, B, Cu, Ni, V,Mo, Mn, etc., and where the oxide may be TiO_(x), SiO_(x), B₂O₃, W₂O₅,Ta₂O₅, NbO₂, CoO, Co₃O₄, etc. A magnetic recording layer having grainsseparated by an oxide segregant may be referred to herein as an oxidemagnetic recording layer.

In various approaches, the average center-to-center spacing (pitch) ofthe grains in the magnetic recording layer structure 724 may be lessthan or equal to about 8.3 nm. In further approaches, the average grainsize in the magnetic recording layer structure 724 may be in a rangefrom about 6 nm to about 8.5 nm.

In some approaches, a thickness of the first magnetic recording layer726 may be greater than or equal to about 5 nm. In particularapproaches, a thickness of the first magnetic recording layer 726 may bein a range from about 5 nm to about 8 nm, preferably in a range fromabout 6 nm to about 7 nm. In other approaches, a thickness of the firstmagnetic recording layer 726 may be greater than or about equal to 40%of the total thickness of the magnetic recording layer structure 724.

In more approaches, the thicknesses of the second, third and fourthmagnetic recording layers 730, 734, 738 may each independently be in arange from 0.5 nm to about 3 nm. In some approaches, some or all of thesecond, third and fourth magnetic recording layers 730, 734, 738 mayhave thicknesses that are the same or different as one another. However,in preferred approaches, a thickness of one or more of the second,third, and fourth magnetic recording layers 730, 734, 738 may be about 1nm.

In preferred approaches, the magnetic anisotropy energy, K_(u), of thefirst magnetic recording layer 726 may be greater than or about equal tothe K_(u) of the second magnetic recording layer 730 and/or the K_(u) ofthird magnetic recording layer 734. For instance, in one approach, themagnetic anisotropy field, H_(k), of the first magnetic recording layer726 may be greater than or equal to about 20 kOe. In more approaches,the H_(k) of the second magnetic recording layer 730 and/or thirdmagnetic recording layer 734 may be in a range from 15 kOe to 20 kOe.

In yet more approaches, the K_(u) of the fourth magnetic recording layer738 may also be greater than or about equal to the K_(u) of the secondmagnetic recording layer 730 and/or the K_(u) of the third magneticrecording layer 734. In still more approaches, the K_(u) of the fourthmagnetic recording layer 738 may be about equal to or less than theK_(u) of the first magnetic recording layer 726. In particularapproaches, the H_(k) of the fourth magnetic recording layer 738 may bein a range from 15 kOe to 22 kOe.

As noted above, the second and third magnetic recording layers 730, 734may each have a K_(u) that is less than the K_(u) values of the firstand/or fourth magnetic recording layers 726, 738 in some approaches.Accordingly, in approaches where the first, second, third and fourthmagnetic recording layers 726, 730, 734, 738 comprise CoCrPt+O₂ and/oroxide, the second and third magnetic layers 730, 734 may each comprise ahigher percentage of at least one of Cr, O₂ and/or the oxide (e.g.,TiO_(x), SiO_(x), B₂O₃, W₂O₅, Ta₂O₅, NbO₂, CoO, Co₃O₄, etc.), and othernon-magnetic materials (e.g., Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn,etc.,) to reduce their respective K_(u) values compared to the K_(u)values of the first and/or fourth magnetic recording layers 726, 738.Moreover, it is important to note that while the second and thirdmagnetic recording layers 730, 734 may each have a K_(u) that is lessthan the K_(u) values of the first and/or fourth magnetic recordinglayers 726, 738 in some approaches, the K_(u) values of the second andthird magnetic recording layers 730, 734 may, but need not, be equal.For instance, the K_(u) of the second magnetic recording layer 730 maybe greater than, equal to, or less than the K_(u) of the third magneticrecording layer 734 in further approaches.

A summary of some of the possible relationships between the H_(k) valuesof the first magnetic recording layer 726 (H_(k)1), the second magneticrecording layer 730 (H_(k)2), the third magnetic recording layer 734(H_(k)3) and the fourth magnetic recording layer 738 (H_(k)4) may berepresented as follows:H_(k)1≥H_(k)4≥H_(k)2≥H_(k)3;H_(k)1≥H_(k)4≥H_(k)3≥H_(k)2.

As noted above, the magnetic recording layer structure 724 of FIG. 7Aincludes at least four exchange coupling layers 728, 732, 736, 740. Theexchange coupling layers 728, 732, 736, 740 are configured tomagnetically decouple the magnetic recording layers 726, 730, 734, 738,as well as promote the grain growth and crystalline orientation of thelayers formed thereabove.

In various approaches, the exchange coupling layers 728, 732, 736, 740are positioned in an upper portion 742 of the magnetic recording layerstructure 724, wherein a thickness of the upper portion 742 may be lessthan or about equal to 60% of the total thickness, t_(mrl), of themagnetic recording layer structure 724.

Each of the exchange coupling layers 728, 732, 736, 740 may include aplurality of grains separated from one another via a segregant material.In numerous approaches, the grains of one or more of the exchangecoupling layers 728, 732, 736, 740 may include one or more of the samematerials (e.g., Co, Cr, Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V,Nb, Ge, B, Pd, etc.) included in the grains of one or more of themagnetic recording layers 726, 730, 734, 738. In additional approaches,the segregant material of one or more of the exchange coupling layers728, 732, 736, 740 may include one or more of the same materials (e.g.,O₂, at least one oxide of Ta, W, Nb, V Mo, B, Si, Co Cr, Ti, Al, etc.)included in the segregant material of one or more of the magneticrecording layers 726, 730, 734, 738. An exchange coupling layer havinggrains separated by an oxide segregant may be referred to herein as anoxide exchange coupling layer.

It is important to note that each of the exchange coupling layers 728,732, 736, 740 are preferably nonmagnetic, e.g., have a saturationmagnetization, M_(s), less than or equal to about 100 emu/cc. Thus, oneor more of the exchange coupling layers 728, 732, 736, 740 may includeone or more of the same materials as one or more of the magneticrecording layers 726, 730, 734, 738, though not necessarily in the samestoichiometric proportions. For example, in some approaches, at leastone of the exchange coupling layers and at least one of the magneticrecording layers may include CoCrPtX+O and/or oxide, where X may be Ta,Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn, etc., and where the oxide may includeone or more of TiO_(x), SiO_(x), B₂O₃, W₂O₅, Ta₂O₅, NbO₂, CoO, Co₃O₄,etc.; however, the amount of Co in the exchange coupling layer may beless than the amount of Co in the magnetic recording layer. Further, anamount of Co in the first magnetic recording layer 726 is greater thanor about equal to the Co amount in the second, third and fourth magneticrecording layers 730, 734, and 738.

In various approaches, the thicknesses of the exchange coupling layers728, 732, 736, 740 may each independently be in a range from about 0.5nm to about 2 nm. In some approaches, some or all of the exchangecoupling layers 728, 732, 736, 740 may have thicknesses that are thesame or different as one another. For instance, in particularapproaches, the thickness of the second exchange coupling layer 732 maybe less than, equal to, or greater than the thickness of third exchangecoupling layer 736.

In more approaches, the thickness of the second exchange coupling layer732 may be greater than the thickness of the first exchange couplinglayer 728 and/or the thickness of the fourth exchange coupling layer740. In yet more approaches, the thickness of the third exchangecoupling layer 736 may be greater than the thickness of the firstexchange coupling layer 728 and/or the thickness of the fourth exchangecoupling layer 740. In still more approaches, the thickness of the firstexchange coupling layer 728 may be less than the thicknesses of allother exchange coupling layers. In still more approaches, the thicknessof the first exchange coupling layer 728 may be about equal to thethickness of the fourth exchange coupling layer 740. In one preferredapproach, the thickness of the first exchange coupling layer 728 may beabout 0.6 nm; the thickness second exchange coupling layer 732 may beabout 1 nm; the thickness of the third exchange coupling layer 736 maybe about 1 nm; and the thickness of the fourth exchange coupling layer740 may be about 0.7 nm.

In further approaches, grains in the magnetic recording layers 726, 730,734, 738 and the exchange coupling layers 728, 732, 736, 740 may have acolumnar shape. Moreover, the grains in each of the magnetic recordinglayers 726, 730, 734, 738 and the exchange coupling layers 728, 732,736, 740 may be physically characterized by growth directly on thegrains present in the layers thereabove and/or therebelow. For instance,each of the grains in the fourth exchange coupling layer 740 may beformed directly on the grains in the fourth magnetic recording layer738, which in turn may be formed directly on the grains in the thirdexchange coupling layer 736 and so on.

It is important to note that while the magnetic recording layerstructure 724 of FIG. 7A includes five magnetic recording layers 726,730, 734, 738, 744 and four exchange coupling layers 728, 732, 736, 740,the magnetic recording layer structure 724 may include one or moreadditional magnetic recording layers and one or more additional exchangecoupling layers in various approaches. For instance, as shown in FIG.7B, a perpendicular magnetic recording medium 701 may include a magneticrecording layer structure 748 having six or more magnetic recordinglayers and five or more exchange coupling layers, where the magneticrecording layers and the exchange coupling layers are arranged in analternating pattern. As FIG. 7B depicts one exemplary variation of theperpendicular magnetic recording medium 700 of FIG. 7A, components andlayers of FIG. 7B have common numbering with those of FIG. 7A. It isimportant to note, however, that the fifth magnetic recording layer 744shown in FIG. 7A, is represented as the sixth magnetic recording layer744 in FIG. 7B.

With continued reference to FIG. 7A, the fifth magnetic recording layer744 (also referred to as the cap layer 744) may form the uppermost layerin the magnetic recording layer structure 724. Suitable materials forthe fifth magnetic recording layer (cap layer) 744 may include, but arenot limited to, a Co—, CoCr—, CoPtCr—, and/or CoPtCrB— based alloy, orother such material as would become apparent to one having skill in theart upon reading the present disclosure. In various approaches, thefifth magnetic recording layer (cap layer) 744 may be a continuous caplayer that does not include a segregant material. For instance, in oneapproach, the fifth magnetic recording layer (cap layer) 744 may notinclude any oxides. In some approaches, the fifth magnetic recordinglayer (cap layer) 744 may be doped with a small amount of oxygen. Forexample, in particular approaches, the fifth magnetic recording layer(cap layer) 744 may be a continuous, partially oxidized cap layer formedat a lower argon pressure than all other magnetic recording layerspositioned therebelow, thus forming a cap layer that is continuous, orat least more continuous than all other magnetic recording layers in themagnetic recording layer structure 724.

In more approaches, a thickness of the fifth magnetic recording layer(cap layer) 744 may be in a range from about 2 nm to about 5 nm. Inpreferred approaches the thickness of the fifth magnetic recording layer(cap layer) 744 may be about 3 nm. In yet more approaches, the fifthmagnetic recording layer (cap layer) 744 may comprise multiple layersconfigured to achieve ideal separation, magnetics and smoothness.

In additional approaches, the magnetic anisotropy energy, K_(u), of thefifth magnetic recording layer (cap layer) 744 may be less than or aboutequal to the K_(u) of the first and/or fourth magnetic recording layers726, 736. Moreover, while the second, third, and fifth magneticrecording layers 730, 734, 744 may each have a K_(u) that is less thanthe K_(u) values of the first and/or fourth magnetic recording layers726, 738 in some approaches, the K_(u) values of the second, third andfifth magnetic recording layers 730, 734, 744 may, but need not, beequal. For instance, the K_(u) of the fifth magnetic recording layer 730may be greater than, equal to, or less than the K_(u) of the secondand/or third magnetic recording layers 730, 734 in further approaches.In particular approaches, the H_(k) of the fifth magnetic recordinglayer (cap layer) 744 may be in a range from 10 kOe to 18 kOe.

As shown in FIG. 7A, a protective overcoat layer 746 is formed above thefifth magnetic recording layer (cap layer) 744. The protective overcoatlayer may be configured to protect the underlying layers from wear,corrosion, etc. This protective overcoat layer may be made of, forexample, diamond-like carbon, carbon nitride, Si-nitride, BN or B4C,etc. or other such materials suitable for a protective overcoat as wouldbecome apparent to one having skill in the art upon reading the presentdisclosure.

In additional approaches, an optional lubricant layer (not shown in FIG.7A) may be formed above the protective overcoat layer 746. The materialof the lubricant layer may include, but is not limited toperfluoropolyether, fluorinated alcohol, fluorinated carboxylic acids,etc., or other suitable lubricant material as known in the art.

As is described in greater detail below, it has been surprisingly andunexpectedly found that the perpendicular magnetic recording medium 700having at least five magnetic recording layers 726, 730,734, 738, 744and at least four exchange coupling layers 728, 732, 736, 740 exhibitsimproved magnetic recording characteristics (e.g., signal-to-noise ratio(SNR), overwrite (OW), magnetic core width (MCW), etc.) as compared to aperpendicular magnetic recording medium having four or less magneticrecording layers and three or less exchange coupling layers (e.g., asshown in FIG. 6). The improvement in the magnetic recordingcharacteristics, such as the OW, for the perpendicular magneticrecording medium 700 of FIG. 7 is indeed surprising and unexpected giventhe increase in overall thickness of the magnetic recording layerstructure 724 (e.g., via addition of at least one additional magneticrecording layer and at least one addition exchange coupling layer, andincorporation of a thicker, high K_(u) lowermost magnetic recordinglayer) relative to the magnetic recording layer structure 624 of theperpendicular magnetic recording medium 600 shown in FIG. 6. Rather, oneskilled in the art would typically expect that increasing the thicknessof the lowermost, high Ku magnetic recording layer, and/or adding atleast one more magnetic recording layer and at least one more exchangecoupling layer, both of which ultimately increase the distance betweenthe magnetic head and the lowermost magnetic recording layer, wouldactually degrade media writeability.

Experimental Data and Comparative Examples

The following experimental data describe features and/or characteristicsassociated with the novel perpendicular magnetic storage media disclosedherein, particularly those having a magnetic recording layer structurecomprising five magnetic recording layers and four exchange couplinglayers as shown FIG. 7A. A perpendicular magnetic recording mediumhaving a magnetic recording layer structure with five magnetic recordinglayers and four exchange coupling layers may be referred to as a “quadECL structure” or “Q-ECL” for clarity.

Comparative examples are also provided to illustrate the differencesbetween quad ECL structures and triple ECL (T-ECL) structures (i.e.,perpendicular magnetic recording media having a magnetic recordingstructure with four magnetic recording layers and three exchangecoupling layers as shown FIG. 6).

Also for clarity, the lowermost magnetic recording layer in a quad ECLstructure (e.g., the first magnetic recording layer 726 shown in FIG.7A) may be referred to as the “G0” layer, whereas the lowermost magneticrecording layer in a triple ECL structure (e.g., the first magneticrecording layer 626 shown in FIG. 6) may be referred to as the “G1”layer. Additionally, the media grain pitch in a quad or triple ECLstructure corresponds to the average grain pitch in the magneticrecording layer structure present therein (e.g., the magnetic recordinglayer structure 724 shown in FIG. 7A for the quad ECL structure; and themagnetic recording layer structure 624 shown in FIG. 6 for the tripleECL structure).

It is important to note that the experimental data and comparativeexamples do not limit the invention in anyway.

FIGS. 8-12 provide plots illustrating the relationship between variousmeasured magnetic characteristics and media grain pitch for four quadECL structures with different G0 thicknesses. These measure magneticcharacteristics include: the coercivity, H_(c), (FIG. 8); the nucleationfield, H_(n), (FIG. 9); the switching field distribution, SFD (FIG. 10);the thermal stability factor, K_(u)V/k_(B)T, (FIG. 11); and theintrinsic switching field distribution, iSFD, (FIG. 12). As discussedpreviously, to achieve an areal recording density of at least 1Tbit/in², a grain pitch of about 8 nm or less is needed. However,decreasing grain pitch may also result in degrading the aforementionedmagnetic characteristics, e.g., H_(c) decreases, H_(n) increases, SFDincreases, K_(u)V/k_(BT) decreases, and iSFD increases. Despite thenegative effects associated with decreasing grain pitch, increasing thethickness of the G0 layer to be in a range from about 6 nm to about 7.4nm when the grain pitch is about 8 nm or less nonetheless yields desiredvalues for H_(c), H_(n), SFD, K_(u)V/k_(B)T, and iSFD, as shown in FIGS.8-12.

FIG. 13 provides a plot illustrating the relationship between magneticcluster size and media grain pitch for four quad ECL structures withdifferent G0 thicknesses. One having skill in the art would notnecessarily expect the magnetic cluster size, corresponding to thereversal unit of magnetization in the granular magnetic recording layer,to continually decrease with decreasing grain size and pitch. Forinstance, a plot of magnetic cluster size versus grain pitch for atriple ECL structure typically exhibits a “cluster size knee”characteristic of a cluster size that initially decreases with grainpitch until a particular grain pitch is reached, after which the clustersize increases as the grain pitch continues to decrease. However, it hasbeen surprisingly and unexpectedly found that for quad ECL structureshaving a G0 layer with a thickness in a range from about 6 nm to about7.4 nm, the magnetic cluster size continually decreases with decreasinggrain pitch and thus does not exhibit a cluster size knee.

FIG. 14 shows a plot illustrating the relationship between overwrite(OW) and media grain pitch for four quad ECL structures with differentG0 thicknesses and a triple ECL structure. As shown in FIG. 14, the OWdoes not significantly vary with grain size and pitch; however, the OWdoes strongly depend on G0 thickness. Moreover, FIG. 14 highlights thesurprising and unexpected results that quad ECL structures having a G0layer with a thickness in a range from about 6 nm to about 7.4 nmexhibit comparable or superior OW results compared to the triple ECLstructure having a G1 layer with a thickness of about 5 nm.

FIG. 15 shows a plot illustrating the relationship between magnetic corewidth (MCW) and media grain pitch for four quad ECL structures withdifferent G0 thicknesses and a triple ECL structure. In particular, FIG.15 provides a plot of the 6 TMCW versus grain pitch. Frequency T (or 1T) is the highest linear frequency for a particular PMR medium. Forexample, if 1 T=1460 kfci, 2 T indicates that the frequency is half ofthe IT frequency (i.e., 2 T=730 kfci), and 6 T would be ⅙ of the ITfrequency (e.g., 6 T=about 243 kfci). Accordingly, 6 TMCW is themagnetic core width at frequency T/6.

As shown in FIG. 15, while the 6 TMCW does not significantly vary withgrain size, it does strongly depend on G0 thickness. FIG. 15 furtherhighlights that quad ECL structures having a G0 layer with a thicknessin a range from about 6 nm to about 7.4 nm exhibit a comparable orsuperior 6 TMCW compared to the triple ECL structure having a G1 layerwith a thickness of about 5 nm.

FIGS. 16-18 show several plots illustrating the relationship betweenSoNR and media grain pitch for four quad ECL structures with differentG0 thicknesses and a triple ECL structure. In particular, FIG. 16provides a plot of 6 TSoNR versus grain pitch; FIG. 17 provides a plotof 2 TSoNR versus grain pitch; and FIG. 18 provides a plot of 1 TSoNRversus grain pitch. SoNR refers to the spectral signal-to-noise ratio ata fixed signal measured at a fixed linear density. Stated another way,SoNR refers to the low frequency signal (So) [measured at about 100 kfci(kiloflux changes per inch)] over the integrated noise power at afrequency of T. As noted above, frequency T (or 1 T) is the highestlinear frequency for a particular PMR medium. Accordingly, 1 TSNR is thespectral signal-to-noise ratio of the signal (S) (at a frequency T) overthe integrated noise power at a frequency of T; 2 TSNR is the spectralsignal-to-noise ratio of the signal (S) (at a frequency T/2) over theintegrated noise power at a frequency of T/2; and 6 TSNR is the spectralsignal-to-noise ratio of the signal (S) (at a frequency T/6) over theintegrated noise power at a frequency of T/6.

SoNR measurements differ from SNR measurements only in that the signalused for the SoNR corresponds to the low frequency signal, So. SoNRmeasurements provide a better sense of how the noise alone increaseswith increasing frequency, whereas SNR measurements combines the signalrolloff (signal decreases with increasing frequency) and the integratednoise increase with increasing linear frequency.

As shown in FIGS. 16-17, there is no significant variation in the 6TSoNR and 2 TSoNR for different grain pitch values; however, adependence between the G0 thickness and the 6 TSoNR, 2 TSoNR is evident.In particular, FIGS. 16-17 highlight that quad ECL structures having aG0 layer with a thickness preferably in a range from about 6 nm to about7 nm exhibit a comparable or superior 6 TSoNR and 2 TSoNR compared tothe triple ECL structure having a G1 layer with a thickness of about 5nm.

FIG. 18 illustrates that the SoNR at the highest linear density (1TSoNR) does vary with grain pitch to a greater extent than the 6 T SoNRand 2 T SoNR. Similar to FIGS. 16-17, FIG. 18 also illustrates adependence between G0 thickness and 1 TSoNR, where quad ECL structureshaving a G0 layer with a thickness preferably in a range from about 6 nmto about 7 nm exhibit a comparable or superior 1 TSoNR compared to thetriple ECL structure having a G1 layer with a thickness of about 5 nm.

FIGS. 19-20 show several plots illustrating the relationship betweenSoNR and MCW for four quad ECL structures with different G0 thicknessesand a triple ECL structure. In particular, FIG. 19 provides a plot of 2TSoNR versus 6 TMCW, and FIG. 20 provides a plot of 1 TSoNR versus 6TMCW. FIGS. 19 and 20 highlight the dependence between MCW and G0thickness, as well as the comparable and superior 1 TSoNR and 2 TSoNRvalues for quad ECL structures having a G0 layer with a thicknesspreferably in a range from about 6 nm to about 7 nm as compared to thetriple ECL structure having a G1 layer with a thickness of about 5 nm.

FIGS. 21-22 show several plots illustrating the relationship betweenSoNR and MCW for a quad ECL structure compared to two triple ECLstructures. Specifically, FIG. 21 provides a plot of 2 TSoNR versus 6TMCW, and FIG. 22 provides a plot of 1 TSoNR versus 6 TMCW. Moreover,for FIGS. 21-22, the quad ECL structure (corresponding to the circularindicators) has a media grain pitch of 8.1 nm and a 6.3 nm thick G0layer; the triple ECL structure (corresponding to the square indicator)has a media grain pitch of 8.7 nm and a 5.3 nm thick G1 layer; and thetriple ECL structure (corresponding to the triangular indicator) has amedia grain pitch of 8.8 nm and a 5.1 nm thick G1.

FIG. 23 shows a plot illustrating the relationship between OW and G0thickness for three quad ECL structures with different EBL structurethicknesses and a triple ECL structure. The EBL structure thicknessesfor each ECL structure shown in FIG. 23 is as follows:

-   Triple ECL structure (square indicators): 17 nm-   Quad ECL structure (circular indicators): 17 nm-   Quad ECL structure+EBL (triangular indicators): 15 nm-   Quad ECL structure+thinner EBL (star indicators): 13 nm.    As shown in FIG. 23, each of the quad ECL structures having G0    thicknesses up to about 6.5 nm exhibit superior results in    writeability as compared to the triple ECL structure. However, it is    of note that the writeability advantage for the quad ECL structure    corresponding to the circular indicators may begin to decrease for    G0 thicknesses greater than about 6.5 nm due to the greater overall    thickness of the quad ECL structure. Accordingly, as also shown in    FIG. 23, reducing the thickness of the EBL structure in the quad ECL    structures further improves writeability.

FIGS. 24-27 show plots illustrating the relationship between variousmeasured magnetic characteristics and overall thickness of the SULstructure for two quad ECL structures and a triple ECL structure. Thesemeasure magnetic characteristics include: OW (FIG. 24); MCW (FIG. 25); 2TSoNR (FIG. 26); and 1 TSoNR (FIG. 27). The two quad ECL structuresshown in FIGS. 24-27 have a G0 thickness of about 6.3 nm, whereas thetriple ECL structure has a G1 thickness of about 5.3 nm. Additionally,the two quad ECL structures have different cap layer compositions thatdiffer primarily with regard to the amount of O₂ flowing during thesputtering deposition. Particularly, the quad ECL structure representedby the square indicators in FIGS. 24-27 has a cap layer with a highermoment than the quad ECL structure represented by the circularindicators.

Review of FIGS. 24-27 reveals that the quad ECL structures having a SULstructure with a thickness in a range from about 12 nm to about 25 nmexhibit comparable or superior OW results compared to the triple ECLthat has a 30 nm thick SUL structure. Moreover, the quad ECL structureshaving a SUL structure with a thickness in a range from about 12 nm toabout 25 nm exhibit a comparable or narrower MCW while still maintaininggood SoNR.

Referring now to Table 1 below, several measurements of recordingcharacteristics are shown for a triple ECL structure and three quad ECLstructures. Each of the quad ECL structures (A-C) have a 6.3 nm thick G0layer; whereas the triple ECL structure has a 5.3 nm thick G1 layer.Moreover, the primary difference between the three quad ECL structures(A-C) corresponds to the degree of lateral exchange coupling in the caplayer, with quad ECL B having a cap layer with a greater degree oflateral exchange coupling than quad ECL A, and quad ECL C having thegreatest degree of lateral exchange coupling as compared to quad ECL Aand quad ECL B.

It is evident from Table 1, that the quad ECL structures exhibitcomparable or superior recording characteristics as compared to thetriple ECL structure. For example, a comparison between the quad ECLstructure A and the triple ECL structure reveals that the quad ECLstructure A exhibits about 0.1 order N-SER gain, about the same OW, anarrower MCW and greater than about 1% ADC_FOM gain.

TABLE 1 Recording Parametric Measurements Triple ECL Quad ECL A Quad ECLB Quad ECL C 6TMCW (nm) 66.3 64.8 67.1 66.8 N-SER (nm) −5.03 −5.18 −5.00−5.12 ADC_FOM 668.6 679.0 679.1 675.4 EB (nm) 3.07 3.40 3.22 3.20 N-OW(nm) 30.9 30.8 33.3 33.1 2T SoNR 32.0 32.0 32.4 32.5 T50 19.46 20.0620.04 19.53

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

It should also be noted that methodology presented herein for at leastsome of the various embodiments may be implemented, in whole or in part,in computer hardware, software, by hand, using specialty equipment, etc.and combinations thereof.

Moreover, any of the structures and/or steps may be implemented usingknown materials and/or techniques, as would become apparent to oneskilled in the art upon reading the present specification.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

The invention claimed is:
 1. A magnetic recording medium comprising: a recording layer structure comprising: a first magnetic recording layer; a second magnetic recording layer; a third magnetic recording layer; a fourth magnetic recording layer; and a plurality of nonmagnetic exchange coupling layers, wherein the first magnetic recording layer is closest to a substrate and the fourth magnetic recording layer is farthest from the substrate; and wherein an amount of Co in the first magnetic recording layer is greater than or equal to the amount of Co in the second magnetic recording layer, the third magnetic recording layer, and the fourth magnetic recording layer.
 2. The magnetic recording medium of claim 1, wherein the plurality of nonmagnetic exchange coupling layers comprises: a first nonmagnetic exchange coupling layer between the first magnetic recording layer and the second magnetic recording layer; a second nonmagnetic exchange coupling layer between the second magnetic recording layer and the third magnetic recording layer; a third nonmagnetic exchange coupling layer between the third magnetic recording layer and the fourth magnetic recording layer; and a fourth nonmagnetic exchange coupling layer above the fourth magnetic recording layer.
 3. The magnetic recording medium of claim 1, further comprising a fifth magnetic recording layer above the fourth magnetic recording layer.
 4. The magnetic recording medium of claim 1, wherein each of the plurality of nonmagnetic exchange coupling layers comprises a CoCrPtX-oxide material, wherein X comprises at least one of Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn.
 5. The magnetic recording medium of claim 1, wherein: a magnetic anisotropy field value of the first magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the fourth magnetic recording layer; the magnetic anisotropy field value of the fourth magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the second magnetic recording layer; and the magnetic anisotropy field value of the second magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the third magnetic recording layer.
 6. The magnetic recording medium of claim 1, wherein: a magnetic anisotropy field value of the first magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the fourth magnetic recording layer; the magnetic anisotropy field value of the fourth magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the third magnetic recording layer; and the magnetic anisotropy field value of the third magnetic recording layer is greater than or equal to the magnetic anisotropy field value of the second magnetic recording layer.
 7. A data storage system comprising the magnetic recording medium of claim
 1. 8. A magnetic recording medium comprising: a recording layer structure comprising: a plurality of magnetic recording layers; and a plurality of nonmagnetic exchange coupling layers alternating with the plurality of magnetic recording layers; wherein each of the plurality of nonmagnetic exchange coupling layers comprises Co in an amount that is less than an amount of Co in each of the plurality of magnetic recording layers.
 9. The magnetic recording medium of claim 8, wherein the plurality of magnetic recording layers comprises a first magnetic recording layer that is closest to a substrate, and a thickness of the first magnetic recording layer is greater than or equal to 40% of a total thickness of the recording layer structure.
 10. The magnetic recording medium of claim 8, further comprising a soft magnetic underlayer structure between a substrate and the recording layer structure, wherein the soft magnetic underlayer structure comprises: a first soft magnetic underlayer; a second soft magnetic underlayer; and a coupling layer between the first soft magnetic underlayer and the second soft magnetic underlayer.
 11. The magnetic recording medium of claim 10, further comprising an exchange break layer structure between the soft magnetic underlayer structure and the recording layer structure, wherein the exchange break layer structure comprises: a first exchange break layer; a second exchange break layer above the first exchange break layer; and a third exchange break layer above the second exchange break layer.
 12. A data storage system comprising the magnetic recording medium of claim
 8. 13. A magnetic recording medium comprising: a recording layer structure comprising: a first magnetic recording layer; a second magnetic recording layer disposed above the first magnetic recording layer; a third magnetic recording layer disposed above the second magnetic recording layer; a fourth magnetic recording layer disposed above the third magnetic recording layer; and a plurality of nonmagnetic exchange coupling layers, wherein: an amount of Co in the first magnetic recording layer is greater than or equal to the amount of Co in the second magnetic recording layer, the third magnetic recording layer, and the fourth magnetic recording layer; and a magnetic anisotropy energy of each of the first magnetic recording layer and the fourth magnetic recording layer is greater than a magnetic anisotropy energy of each of the second magnetic recording layer and the third magnetic recording layer.
 14. The magnetic recording medium of claim 13, wherein the recording layer structure further comprises a fifth magnetic recording layer disposed above the fourth magnetic recording layer, wherein a magnetic anisotropy energy of the fifth magnetic recording layer is less than the magnetic anisotropy energy of each of the first magnetic recording layer and the fourth magnetic recording layer.
 15. The magnetic recording medium of claim 13, wherein the first magnetic recording layer comprises a thickness that is greater than or equal to 40% of a total thickness of the recording layer structure.
 16. The magnetic recording medium of claim 13, wherein each of the plurality of nonmagnetic exchange coupling layers comprises a CoCrPtX-oxide material, wherein X comprises at least one of Ta, Si, Ru, Ti, B, Cu, Ni, V, Mo, Mn.
 17. The magnetic recording medium of claim 13, wherein the plurality of nonmagnetic exchange coupling layers each comprise a same material as that of the first magnetic recording layer, the second magnetic recording layer, the third magnetic recording layer, and the fourth magnetic recording layer.
 18. The magnetic recording medium of claim 13, wherein the plurality of nonmagnetic exchange coupling layers comprises: a first nonmagnetic exchange coupling layer between the first magnetic recording layer and the second magnetic recording layer; a second nonmagnetic exchange coupling layer between the second magnetic recording layer and the third magnetic recording layer; a third nonmagnetic exchange coupling layer between the third magnetic recording layer and the fourth magnetic recording layer; and a fourth nonmagnetic exchange coupling layer above the fourth magnetic recording layer.
 19. The magnetic recording medium of claim 18, wherein a thickness of each of the second nonmagnetic exchange coupling layer and the third nonmagnetic exchange coupling layer is greater than a thickness of each of the first nonmagnetic exchange coupling layer and the fourth nonmagnetic exchange coupling layer.
 20. A data storage system comprising the magnetic recording medium of claim
 13. 